1. Field of the Invention
This invention provides a process for converting biomass to useful chemicals or fuels, by anaerobic fermentation of biomass and recovery of useful products from the fermentation medium. By alternative arrangement of the process steps of this invention, a variety of products (i.e. organic acids, ketones, aldehydes, and alcohols) may be produced from biomass. These products are made from salts of the organic acids (e.g., acetate, propionate, butyrate, lactate) that are the primary fermentation products of the fermentation.
2. Review of Related Art
Organic acids are important chemicals of commerce. Historically, organic acids were produced from animal fat or vegetable oil sources or from petroleum sources in substantially nonaqueous systems. More recently, organic acids have been identified as among the most attractive products for manufacture from biomass by fermentation. Biomass can be defined as any animal- or plant-based material of carbohydrate, protein or fat composition. Among the readily available sources of biomass are municipal solid waste (MSW) and sewage sludge (SS). At present, great expenditures of public funds are used to dispose of such wastes, including costs involved in treatment, transport, incineration, or dumping in landfills or oceans. The recovery of valuable products from biomass such as MSW and SS could recover the costs of disposal as well as reduce reliance on nonrenewable fossil fuel resources which serve as feedstock for most industrial organic acid production. Fermentation, therefore, can convert renewable organic materials, now considered a costly waste, into valuable chemical commodities.
However, the acids are produced by the fermentation in dilute aqueous solutions, and recovery of the acids in pure form involves separation from a large quantity of water. This recovery introduces significant operating expense into the process, while the physical plant required to handle the large volumes of solution introduces significant capital expense. The combination of capital and operating expense has, until now, made production of organic acids from biomass uneconomical. Thus, there remains a need for a process that combines unit operations for fermentation, concentration and recovery of organic acids to take advantage of potential synergies obtainable from integrating these processes, thereby generating an economical process for conversion of biomass to useful products.
Ketones, aldehydes, and alcohols predominately are produced from petroleum and natural gas. Because fossil fuels are a finite resource, it is desirable to identify processes that use renewable resources, such as biomass. Biomass-based alcohol production is currently practiced using corn as feedstock; however, because corn has alternative use as food, the feedstock is necessarily costly making the ethanol product expensive. Experimental technologies are being developed in which extracellular enzymes, such as cellulase and hemicellulase, are added to lignocellulosic biomass to produce sugars that are subsequently fermented to ethanol. The primary challenges of this technology are to develop inexpensive sources of enzyme and to develop organisms that can ferment the variety of sugars to ethanol with high yields.
The technology described herein overcomes problems associated with the competing biomass-based technologies by employing mixed cultures of microorganisms that convert the many components of biomass (e.g., cellulose, hemicellulose, pectin, sugar, protein, fats) to organic acids that are subsequently converted to ketones, aldehydes, and alcohols using a variety of chemical steps. Further, the microorganisms produce their own enzymes, thus avoiding the need to add costly extracellular enzymes.